Studer tape end sensor lamp repair

[docb]

I have been slowly working through a Studer A80 VU 1" machine, getting it set up for playing TP running masters. Among the issues I have found so far is a dead lamp in the tape end switch sensor circuit. Unfortunately Studer made this light rather proprietary by potting the lamp in a tubular steel housing with epoxy. The tube mounts in a special bracket and has a glass lens on the end that is intended to shape the beam, which is reflected into a photosensor when the tape runs out.

A little digging through the manual showed that the lamp drops 2.5V and draws about 350mA. A suitable substitute was found in Mouser PN 606-CM8-374 (Chicago Miniature 8-374). Note that this lamp is only rated for 3000 hours. My hunch is that Studer may have used a lamp rated for more like 10,000 hours, but I was not able to find such a lamp in the correct format. I did, however find a white LED, Mouser PN 828-0VLEW1CB9 that looked like it would work. I ordered a few of each type of lamp.

To replace the bulb I cut the lamp housing from its cable harness and then proceeded to dig as much of the epoxy out of the cut end as possible. Eventually we resorted to a series of drill bits of increasing sizes to get the remains of the epoxy and lamp out. There are a couple of plastic insulating sleeves inside, and those were retained for the new lamp. The bits and pieces of the original lamp that were extracted very closely resembled the Chicago Miniature lamp.

Before installing either lamp permanently I decided to try each one to make sure that it would properly trip the sensor switch at the tape end. Both lamps worked well. I decided to use the LED, hoping that it might outlast the incandescent bulb. Put some heat shrink on each lead and put the lamp in the tube with the original plastic sleeves and a dab of Shoe Goo to hold it in place. After a final soldering of the leads to the original harness and installation in the original mounting bracket the sensor should be good as new.

[c1ferrari]

Congratulations, Doc...that must feel very rewarding!

[docb]

Now I am starting on the speed modifications. This is a 3.75/7.5 machine and I need to make a few changes to get it to run at 7.5/15. From there it's on to a general service and some refinishing, and then custom 2 track heads and repro electronics.

[kipdent]

Doc--I wish you were my neighbor! To fix my lamp, I ordered the factory replacement from Audiohouse. Simpler, but more expensive!

Kip

[deeng]

I have a lot of A80 parts including the EOT sensor.  They are not new but could get a machine running.  Contact me if there is something you are looking for.

Scott

[Ki Choi]

Hi Scott:

I am looking for Studer A80RC 1/4" 2 track headblock assembly.  If you have one available for sale, please send me an email with condition and price info.

Thanks,
Ki

[docb]

Doc--I wish you were my neighbor! To fix my lamp, I ordered the factory replacement from Audiohouse. Simpler, but more expensive!

Kip

Out of curiosity - at least in the case of this A80 VU the lamp is attached to the same connector plug as the photosensor. Does the replacement lamp come with leads with pins to fit the plug, or do you have to splice it in to the old leads?

[Ki Choi]

Hi Dan:

Although I had not purchased the lamp alone from Audiohouse, I would guess the part (1.080.300.03) would come with pig tails and one would need to crimp the connectors.  The plug is Molex type and would be pretty easy to replace.

Ki

[deeng]

Hi Ki,

I do have a two track head assembly for the A80.  PM me at deeng01 at gmail dot com to discuss.

Scott

[c1ferrari]

Hi Ki,

I do have a two track head assembly for the A80.  PM me at deeng01 at gmail dot com to discuss.

Scott

Oooh -- I can sense Ki's excitement :-)

-Sam

[kipdent]

Doc--

The factory lamp comes with pigtail leads; we just crimped on the molex connectors and plugged it in.

Kip

[docb]

LED started strobing when I turned it on today. I'll dig a little deeper and post my findings.

[docb]

Follow up - the strobing seemed to indicate that I would need to replace the resistors used in the voltage divider that supplies the lamp. The stock circuit uses a big 10 ohm (IIRC) 4W wirewound resistor in parallel with a 68 ohm 1/4W carbon comp, that works out to around 8 ohms, dropping about 2.8V to leave the 2.5V required for the 350 mA incandescent lamp.  Some quick calcs showed I would need more like a 120 ohm 1/4W to get to the 3.2 or so volts needed for the LED with its much lower current draw.

I wimped out and installed the incandescent lamp instead. Part of the reason is that the filament inside the incandescent lamp creates an oval shaped pattern on the tape, vs. a circle from the LED. The manual explains that the oval shape is to be adjusted horizontally, so that it projects only onto the tape and not below the edge of it where it might reflect back into the sensor even with the tape threaded. In practice the sensor worked just fine with either lamp and I have a few more of each, so I may try adjusting the divider and installing the LED later in the interest of longevity.

As an interesting aside, Paul was mentioning that I should next address the lamps in the motion and direction sensor. He described his A80's pair of grain of wheat bulbs that totally disable the transport when they fail. My machine seems to be either a bit later production or updated, as the light source appears to be really teeny IR LEDs.

[RobinMaldonado]

I have been slowly working through a Studer A80 VU 1" machine, getting it set up for playing TP running masters. Among the issues I have found so far is a dead lamp in the tape end switch sensor circuit. Unfortunately Studer made this light rather proprietary by potting the lamp in a tubular steel housing with epoxy. The tube mounts in a special bracket and has a glass lens on the end that is intended to shape the beam, which is reflected into a photosensor when the tape runs out.

A little digging through the manual showed that the lamp drops 2.5V and draws about 350mA. A suitable substitute was found in Mouser PN 606-CM8-374 (Chicago Miniature 8-374). Note that this lamp is only rated for 3000 hours. My hunch is that Studer may have used a lamp rated for more like 10,000 hours, but I was not able to find such a lamp in the correct format. I did, however find a white led light, Mouser PN 828-0VLEW1CB9 that looked like it would work. I ordered a few of each type of lamp.

To replace the bulb I cut the lamp housing from its cable harness and then proceeded to dig as much of the epoxy out of the cut end as possible. Eventually we resorted to a series of drill bits of increasing sizes to get the remains of the epoxy and lamp out. There are a couple of plastic insulating sleeves inside, and those were retained for the new lamp. The bits and pieces of the original lamp that were extracted very closely resembled the Chicago Miniature lamp.

Before installing either lamp permanently I decided to try each one to make sure that it would properly trip the sensor switch at the tape end. Both lamps worked well. I decided to use the LED, hoping that it might outlast the incandescent bulb. Put some heat shrink on each lead and put the lamp in the tube with the original plastic sleeves and a dab of Shoe Goo to hold it in place. After a final soldering of the leads to the original harness and installation in the original mounting bracket the sensor should be good as new.

Nicely done.. I was searching for such information and finally I got it..